Atomic Theory

1. Atomic Theory The Movers and Shakers of the Subatomic World.

2. Democritus • 440 B.C.E • All matter is made up of atoms, which are indivisible • he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible)

3. Dalton • In the early 1800’s, the English chemist John Dalton did a number of experiments that eventually led to the acceptance of the idea of atoms.

4. Dalton’s Atomic Theory • All elements are composed of atoms. Atoms are solid small spheres and indivisible particles.

5. continued... • Atoms of the same element are exactly alike. HH

6. continued... • Atoms of differentelements are different. O H

7. continued... • Compounds are formed by the joining of atoms of two or more elements. H H O

8. Questions... • What were the four parts of the Dalton’s atomic theory? • Say it again...

9. Was he right? • Dalton’s atomic theory of matter became one of the foundations of chemistry. • BUT it needed work…other scientists had to modify the theory.

10. Thomson • In 1897, the work of an English scientist J. J. Thompson provided the first hint that atoms were made up of even smaller particles • Atoms are divisible…Dalton was wrong!

11. Thompson’s Model • He stated that atoms are made up of positively (+) and negatively (-) charged particles

12. And... • He thought the positive(+) and negative (-) particles were s p r e a d o u t in atoms likep p u l d u d m i s n • (plums inpuddin’)

14. Questions... • What kind of particles did Thompson find in atoms? • What did his idea of an atom look like?

15. Was Thomson Right? • Not really…there arepositively(+) and negatively (-) charged particles inside atoms. • BUT...

16. Rutherford’s Model • In 1908, Rutherford discovered the nucleus. • He stated that atoms have a small, dense, positively (+) charged center called a nucleus.

17. The Nuclear Atom 21/10/2019 . Alpha Particle Scattering Alpha Source An atom Back Next

18. The Nuclear Atom 21/10/2019 Hesuggested that all of the atom’s positive charge, together with most of its mass, is concentrated in the centre. Alpha particles which travel close to the nucleus are strongly deflected. The degree of deflection depends on how close it approaches. Rutherford’s Model + Back Next

19. The Nuclear Atom 21/10/2019 The nucleus must be very small in comparison to the atom. This will account for the vast majority making it through unaffected. Rutherford’s Model Back Next

21. Questions... • What did Rutherford find inside the atom? • What did Rutherford’s atom look like?

22. So... • Particles are not spread out like plums in pudding… • Positive particles (protons) are in the center (nucleus). • Where are the negative particles (electrons)?

23. Bohr’s Model • In 1913, Niels Bohr proposed an improvement to Rutherford’s Model: • Electron’s move in definite orbits around the nucleus, like planets around the sun.

24. + Back Next

25. Questions... • What did Bohr propose? • Where were the particles in Bohr’s model of an atom? • What did it look like? • What was special about the electrons in Bohr’s model?

26. Are we there yet? • Bohr’smodel was used for a long time… • BUT...

27. Modern Atomic Model • An atom has a small,positively charged nucleus surrounded by a large region in which there are enough electrons (-) to make the atom neutral (0).

28. E E E E E P P P E P P P P P P P P P E E E E E E

29. Questions... • Do electrons have specific orbits in the modern model? • What does the atom look like in the new model?

30. Make Your Timeline • After the sheet is passed out: • write your name on it! • Fill out the timeline according to date, scientist, notes, and picture (if there is one) for each scientist we went over. • Neatness counts!!!!! • HAVE FUN

31. Bohr’s Atom electrons in orbits nucleus

32. HELIUM ATOM Shell proton N + - + N - neutron electron What do these particles consist of?

33. ATOMIC STRUCTURE Particle Charge Mass proton + ve charge 1 neutron No charge 1 electron -ve charge nil

34. ATOMIC STRUCTURE 2 He Atomic number the number of protons in an atom Chemical Symbol Chemical Name Helium Atomic mass 4 the number of protons and neutrons in an atom number of electrons = number of protons

35. ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. • first shell a maximum of 2 electrons • second shell a maximum of 8 electrons • third shell a maximum of 8 electrons • forth shell a maximum of 8 electrons

36. ELECTRONIC CONFIGURATION With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example; Nitrogen configuration = 2 , 5 2 in 1st shell 5 in 2nd shell 7 N 2+5 = 7 14

37. ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; 20 11 8 Na O Ca a) b) c) 16 23 40 2,8,8,2 2,8,1 2,6 17 14 5 Cl Si B d) e) f) 11 35 28 2,8,7 2,8,4 2,3

38. Bohr Rutherford Diagrams With Bohr Rutherford diagrams, elements and compounds are represented by Dots to show electrons, and circles to show the shells. For example; O Nitrogen N 7 O O N O O 14 O O

39. Bohr Rutherford Diagrams Draw the Bohr Rutherford Diagrams for the following elements; O 8 17 O O Cl a) b) O 35 O 16 O O O O O Cl O O O O O O O O O O O O O O O O O O

40. SUMMARY • The Atomic Number of an atom = number of protons in the nucleus. • The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. • The number of Protons = Number of Electrons. • Electrons orbit the nucleus in shells. • Each shell can only carry a set number of electrons.

41. References • Investigating Science Pearson 9 • Dercho